Modern editing systems for editing time-based media such as video and audio are based on the concept of creating relationships between digitized media and metadata describing this media. Furthermore, users can combine the metadata (such as “masterclips” and “sequences”) into complex time-based and geometry-based structures. Such metadata also may be collected according to projects. As a consequence, relationships between media and metadata, or among metadata, generally are not one-to-one. For example, a masterclip may refer to multiple pieces of media (e.g., at different digitizing qualities). Similarly, a masterclip may be used by multiple sequences. Such relationships typically define a general graph, which is neither acyclic nor directed. Relationships described by a general graph are hard to describe, visualize and navigate.
To navigate relationships among files and directories in a computer, users generally expect to use a tree structure, as in the Explorer interface in the Windows operating system from Microsoft Corporation. Such a tree structure generally is useful when relationships between objects are exclusively parent-child or container-containee one-to-many relationships with no overlap. These relationships are typically acyclic and directed. Thus, tree structures are useful for files systems in which a folder or file belongs in one and only one folder. A tree structure does not adequately describe the multiple relationships present in a media/metadata environment.